diff --git a/app/src/main/java/org/tasks/caldav/CaldavCalendarSettingsActivity.kt b/app/src/main/java/org/tasks/caldav/CaldavCalendarSettingsActivity.kt
index fe121e71f..7cc1c4fdd 100644
--- a/app/src/main/java/org/tasks/caldav/CaldavCalendarSettingsActivity.kt
+++ b/app/src/main/java/org/tasks/caldav/CaldavCalendarSettingsActivity.kt
@@ -69,10 +69,13 @@ class CaldavCalendarSettingsActivity : BaseCaldavCalendarSettingsActivity() {
                 .setContent {
                     tasksTheme.TasksTheme {
                         val openDialog = rememberSaveable { mutableStateOf(false) }
-                        ShareInviteDialog(openDialog) { email ->
+                        ShareInviteDialog(
+                            openDialog,
+                            email = caldavAccount.serverType != SERVER_OWNCLOUD
+                        ) { input ->
                             lifecycleScope.launch {
                                 // TODO: remove delay hack after beta02 release
-                                email?.let { share(it) } ?: delay(100)
+                                input?.let { share(it) } ?: delay(100)
                                 openDialog.value = false
                             }
                         }
@@ -152,7 +155,7 @@ class CaldavCalendarSettingsActivity : BaseCaldavCalendarSettingsActivity() {
 
         val CaldavAccount.canShare: Boolean
             get() = when (serverType) {
-                SERVER_TASKS, SERVER_SABREDAV -> true
+                SERVER_TASKS, SERVER_OWNCLOUD, SERVER_SABREDAV -> true
                 else -> false
             }
     }
diff --git a/app/src/main/java/org/tasks/caldav/CaldavCalendarViewModel.kt b/app/src/main/java/org/tasks/caldav/CaldavCalendarViewModel.kt
index 05807784d..a668ffa41 100644
--- a/app/src/main/java/org/tasks/caldav/CaldavCalendarViewModel.kt
+++ b/app/src/main/java/org/tasks/caldav/CaldavCalendarViewModel.kt
@@ -94,14 +94,18 @@ class CaldavCalendarViewModel @Inject constructor(
     suspend fun addUser(
         account: CaldavAccount,
         list: CaldavCalendar,
-        email: String
+        input: String
     ) = doRequest {
+        val href = if (account.serverType == CaldavAccount.SERVER_OWNCLOUD)
+            "principal:principals/users/$input"
+        else
+            "mailto:$input"
         withContext(Dispatchers.IO) {
-            provider.forAccount(account, list.url!!).share(account, email)
+            provider.forAccount(account, list.url!!).share(account, href)
         }
         principalDao.insert(Principal().apply {
             this.list = list.id
-            principal = "mailto:$email"
+            principal = href
             inviteStatus = INVITE_UNKNOWN
             access = ACCESS_READ_WRITE
         })
diff --git a/app/src/main/java/org/tasks/caldav/CaldavClient.kt b/app/src/main/java/org/tasks/caldav/CaldavClient.kt
index 6b97bad59..e435c6410 100644
--- a/app/src/main/java/org/tasks/caldav/CaldavClient.kt
+++ b/app/src/main/java/org/tasks/caldav/CaldavClient.kt
@@ -237,31 +237,35 @@ open class CaldavClient(
 
     suspend fun share(
         account: CaldavAccount,
-        email: String,
-        displayName: String? = null,
-        comment: String? = null
+        href: String,
     ) {
         when (account.serverType) {
-            SERVER_TASKS, SERVER_SABREDAV -> shareSabredav(email)
+            SERVER_TASKS, SERVER_SABREDAV -> shareSabredav(href)
+            SERVER_OWNCLOUD -> shareOwncloud(href)
             else -> throw IllegalArgumentException()
         }
     }
 
-    private suspend fun shareSabredav(email: String, displayName: String? = null, comment: String? = null) =
+    private suspend fun shareOwncloud(href: String) =
+        withContext(Dispatchers.IO) {
+            DavCollection(httpClient, httpUrl!!)
+                .post("""
+                    <x4:share xmlns:x4="$NS_OWNCLOUD">
+                        <x4:set>
+                            <x0:href xmlns:x0="$NS_WEBDAV">$href</x0:href>
+                        </x4:set>
+                    </x4:share>
+                """.trimIndent().toRequestBody(MIME_XML)
+                ) {}
+        }
+
+    private suspend fun shareSabredav(href: String) =
         withContext(Dispatchers.IO) {
             DavCollection(httpClient, httpUrl!!)
                 .post("""
                     <D:share-resource xmlns:D="$NS_WEBDAV">
                         <D:sharee>
-                            <D:href>mailto:$email</D:href>
-                            ${displayName?.let { """
-                            <D:prop>
-                                <D:displayname>$it</D:displayname>
-                            </D:prop>
-                            """.trimIndent() }}
-                            ${comment?.let { """
-                            <D:comment>$it</D:comment>
-                            """.trimIndent() }}
+                            <D:href>$href</D:href>
                             <D:share-access>
                                 <D:read-write />
                             </D:share-access>
diff --git a/app/src/main/java/org/tasks/compose/ShareInvite.kt b/app/src/main/java/org/tasks/compose/ShareInvite.kt
index 6ead4e027..14566d225 100644
--- a/app/src/main/java/org/tasks/compose/ShareInvite.kt
+++ b/app/src/main/java/org/tasks/compose/ShareInvite.kt
@@ -13,6 +13,7 @@ import androidx.compose.material.Text
 import androidx.compose.material.darkColors
 import androidx.compose.material.icons.Icons
 import androidx.compose.material.icons.outlined.Email
+import androidx.compose.material.icons.outlined.Person
 import androidx.compose.runtime.Composable
 import androidx.compose.runtime.MutableState
 import androidx.compose.runtime.mutableStateOf
@@ -29,44 +30,45 @@ import org.tasks.compose.ShareInvite.ShareInvite
 @Preview(showBackground = true, backgroundColor = 0xFFFFFF)
 @Composable
 private fun Invite() = MaterialTheme {
-    ShareInvite(mutableStateOf(""))
+    ShareInvite(true, mutableStateOf(""))
 }
 
 @Preview(showBackground = true, backgroundColor = 0x202124)
 @Composable
 private fun InviteDark() = MaterialTheme(darkColors()) {
-    ShareInvite(mutableStateOf(""))
+    ShareInvite(false, mutableStateOf(""))
 }
 
 @Preview(showBackground = true, backgroundColor = 0xFFFFFF)
 @Composable
 private fun InviteFilled() = MaterialTheme {
-    ShareInvite(mutableStateOf("user@example.com"))
+    ShareInvite(true, mutableStateOf("user@example.com"))
 }
 
 @Preview(showBackground = true, backgroundColor = 0x202124)
 @Composable
 private fun InviteDarkFilled() = MaterialTheme(darkColors()) {
-    ShareInvite(mutableStateOf("user@example.com"))
+    ShareInvite(false, mutableStateOf("user@example.com"))
 }
 
 object ShareInvite {
     @Composable
     fun ShareInviteDialog(
         openDialog: MutableState<Boolean>,
+        email: Boolean,
         invite: (String?) -> Unit,
     ) {
-        val email = rememberSaveable { mutableStateOf("") }
+        val text = rememberSaveable { mutableStateOf("") }
         // TODO: remove after beta02 release: https://issuetracker.google.com/issues/181282423
         val enableHack = rememberSaveable { mutableStateOf(true) }
         if (openDialog.value) {
             AlertDialog(
                 onDismissRequest = {},
-                text = { ShareInvite(email, enableHack) },
+                text = { ShareInvite(email, text, enableHack) },
                 confirmButton = {
                     TextButton(text = R.string.invite, onClick = {
                         enableHack.value = false
-                        invite(email.value)
+                        invite(text.value)
                     })
                 },
                 dismissButton = {
@@ -77,29 +79,36 @@ object ShareInvite {
                 },
             )
         } else {
-            email.value = ""
+            text.value = ""
             enableHack.value = true
         }
     }
 
     @Composable
-    fun ShareInvite(email: MutableState<String>, enableHack: MutableState<Boolean> = mutableStateOf(true)) {
+    fun ShareInvite(
+        email: Boolean,
+        text: MutableState<String>,
+        enableHack: MutableState<Boolean> = mutableStateOf(true)
+    ) {
         Column(modifier = Modifier.fillMaxWidth()) {
             Text(
                 stringResource(R.string.share_list),
                 style = MaterialTheme.typography.h6,
             )
             Spacer(Modifier.height(Constants.KEYLINE_FIRST))
+            val label = stringResource(if (email) R.string.email else R.string.user)
             OutlinedTextField(
                 modifier = Modifier.fillMaxWidth(),
-                value = email.value,
-                label = { Text(stringResource(R.string.email)) },
-                keyboardOptions = KeyboardOptions(keyboardType = KeyboardType.Email),
-                onValueChange = { email.value = it },
+                value = text.value,
+                label = { Text(label) },
+                keyboardOptions = KeyboardOptions(
+                    keyboardType = if (email) KeyboardType.Email else KeyboardType.Text
+                ),
+                onValueChange = { text.value = it },
                 leadingIcon = {
                     Icon(
-                        imageVector = Icons.Outlined.Email,
-                        contentDescription = stringResource(id = R.string.email)
+                        imageVector = if (email) Icons.Outlined.Email else Icons.Outlined.Person,
+                        contentDescription = label
                     )
                 },
                 enabled = enableHack.value,